1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, a semiconductor device having a capacitor employing ferroelectrics as a capacitor insulating film and a method of manufacturing the same.
2. Description of the Prior Art
In recent years, in the semiconductor integrated circuit device, miniaturization of a capacitor has been requested according to the high integration density.
Then, in the prior art, an application of material (ferroelectrics, etc.) such as (Sr,Ba)TiO.sub.3, Pb(Zr,Ti)O.sub.3, or the like having a high dielectric constant to a capacitor insulating film of a semiconductor memory device has been expected. Meanwhile, in order to increase an integration degree of DRAM, etc., it is effective to reduce an area of the capacitor. In this case, if a ferroelectrics film which has the high dielectric constant rather than a silicon oxide film, a silicon nitride film, etc. in the prior art is employed as the capacitor insulating film, the area of the capacitor can be reduced. As shown in FIG. 13, normally the ferroelectrics have a perovskite crystal structure and are distinguished into an A site and a B site according to their orientation locations. In (Sr, Ba)TiO.sub.3 and Pb(Zr,Ti)O.sub.3, Sr and Ba, or Pb are oriented at the A site respectively and Ti, or Zr and Ti are oriented at the B site respectively.
FIGS. 1A and 1B are sectional views showing a method of forming a capacitor using the ferroelectrics as the capacitor insulating film in the prior art.
As shown in FIG. 1A, an insulating film 2 is formed on a semiconductor substrate 1 and then a two-layered metal film 3 consisting of a Ti film 301 and a Pt film 302 formed on the Ti film 301 is formed.
Then, a ferroelectrics film 4 made of (Pb,La)(Zr,Ti )O.sub.3 (referred to as "PLZT" hereinafter) is formed and then a Pt film 5 is formed.
Then, as shown in FIG. 1B, an upper electrode 5a made of the Pt film, a capacitor insulating film 4a made of the PLZT film, and a lower electrode 3a made of the two-layered metal film 3 consisting of the Ti film 301 and the Pt film 302 are formed by patterning these films in order of the Pt film 5, the PLZT film 4, and the Ti/Pt film 3 separately. With the above, the capacitor has been completed.
Since the capacitor formed as above has employed the ferroelectrics film as the capacitor insulating film 4a, the area of the capacitor can be reduced and thus such ferroelectrics film would be desired for miniaturization of the device.
However, in the capacitor employing the above material having a high dielectric constant as the capacitor insulating film 4a, the characteristics of the capacitor are changed considerably if the composition is changed.
In other words, there have been the problems that, if the particular composition is employed, the leakage current can be reduced smaller but the hysteresis loop is also reduced smaller. In contrast, there has been the problem that, if the hysteresis loop is enhanced by changing the composition, the leakage current would be increased inevitably.